The Influence of Serotonine and Amphetamine on Analgesic Effect of Morphine after Reserpine Premedication in Rats and Mice

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Abstract
Applying the ultrasound algic stimulus in experiments on mice and rats we have examined the analgesic effect of morphine in subthreshold doses and of both reserpine alone, and in combination with morphine. Reserpine alone had no analgesic effect and it does not increase the analgesic effect of morphine in subthreshold doses. In other series of experiments, the influence of the analgesic effect of morphine in subthreshold doses (mediated through 5-HT) [5-hydroxytryptamine] was investigated in rats. 5-HT potentiated the analgesic action of morphine in doses of 1 mgAg, 10 nag/kg and 20 mg/kg. Reserpine premedication 1, 4 and 24 hours prior to administration of 5-HT and morphine abolishes the analgesia-potentiating effect of 5-HT to the subthreshold level dose of morphine. If reserpine was administered 48 and 72 hours prior to 5-HT application, reserpine did not abolish this effect. The analgesic potentiating action of 5-HT after reserpine was preserved when amphetamine was given prior to the administration of 5-HT and morphine.